Lithium batteries, and lithium secondary batteries among the lithium batteries have characteristics such as a high energy density and a long lifespan, and have been used as a power supply of electric home appliances such as a video camera, portable electronic apparatuses such as a note book computer and a cellular phone, and the like. Recently, the lithium secondary batteries have been applied to a large-sized battery that is mounted on the electric vehicle (EV), the hybrid electric vehicle (HEV), and the like.
The lithium secondary batteries have the following structure. During charging, lithium is eluted from a positive electrode as an ion, moves to a negative electrode, and is intercalated to the negative electrode. In contrast, during discharging, the lithium ion returns to the positive electrode from the negative electrode. It is known that a high energy density of the lithium secondary battery is caused by a potential of a positive electrode material.
As a positive electrode active material of the lithium secondary batteries, in addition to a lithium-manganese oxide (LiMn2O4) having a spinel structure, a lithium metal composite oxide such as LiCoO2, LiNiO2, and LiMnO2 which have a layered structure are known. For example, LiCoO2 has a layered structure in which a lithium atom layer and a cobalt atom layer are alternately laminated through an oxygen atom layer, and thus LiCoO2 has large charge and discharge capacity and is excellent in diffusibility in intercalation and deintercalation of lithium ions. Accordingly, the majority of the lithium secondary batteries which are commercially available are lithium metal composite oxides such as LiCoO2 having a layered structure.
The lithium metal composite oxides such as LiCoCO2 and LiNiO2 which have a layered structure are expressed by General Formula LiMeO2 (Me: transition metal). A crystal structure of the lithium metal composite oxides having the layered structure belongs to a space group R-3m (“-” is typically attached to an upper section of “3” and represents rotary inversion. The same shall apply hereinafter), and a Li ion, a Me ion, and an oxide ion occupy a 3a site, a 3b site, and a 6c site, respectively. In addition, it is known that the structure shows a layered structure in which a layer (Li layer) constituted by the Li ion, and a layer (Me layer) constituted by the Me ion are alternately laminated through an O layer constituted by the oxide ion.
In the related art, with regard to the lithium metal composite oxides (LiMxO2) having a layered structure, for example, Patent Document 1 discloses an active material that is expressed by Formula: LiNxMn1-xO2 (in Formula, 0.7≦x≦0.95). The active material is obtained as follows. An alkali solution is added to a mixed aqueous solution of manganese and nickel so as to allow manganese and nickel to coprecipitate, lithium hydroxide is added to the resultant mixture, and then calcining is performed.
Patent Document 2 discloses a positive electrode active material which is constituted by crystal grains of oxides including three kinds of transition metals and is expressed by Li[Lix(APBQCR)1-x]O2 (in Formula, A, B, and C represent three different kinds of transition metal elements, −0.1≦x≦0.3, 0.2≦P≦0.4, 0.2≦Q≦0.4, and 0.2≦R≦0.4), and in which a crystal structure of the crystal grains is a layered structure and arrangement of oxygen atoms that constitute the oxides is cubic closest packing.
Patent Document 3 discloses a method of producing a layered lithium-nickel-manganese composite oxide powder so as to provide the layered lithium-nickel-manganese composite oxide powder having a high volume density. The method includes a step of drying slurry through spray dry, the slurry containing at least a lithium source compound, a nickel source compound, and a manganese source compound, which are pulverized and mixed-in, in a molar ratio [Ni/Mn] of a nickel atom [Ni] and a manganese atom [Mn] which is set to a range of 0.7 to 0.9, a step of calcining the resultant dried object to obtain a layered lithium-nickel-manganese composite oxide powder, and a step of pulverizing the composite oxide powder.
Patent Document 4 discloses a material which contains a lithium transition metal composite oxide which has a crystallite diameter enlarged through mixing-in of vanadium (V) and/or boron (B), that is, a lithium transition metal composite oxide expressed by General Formula LixMyOz-δ (In Formula, M represents Co or Ni which is a transition metal element, and relationships of (X/Y)=0.98 to 1.02, and (δ/Z) 0.03 are satisfied), and contains vanadium (V) and/or boron (B) in a ratio of ((V+B)/M)=0.001 to 0.05 (molar ratio) with respect to the transition metal element (M) that constitutes the lithium transition metal composite oxide, and in which a primary particle size is equal to or greater than 1 μm, the crystallite diameter is equal to or greater than 450 Å, and lattice distortion is 0.05% or less.
Patent Document 5 is aimed at providing a positive electrode active material for a nonaqueous secondary battery which is constituted by primary particles capable of maintaining a high volume density or high battery characteristics without anxiety for occurrence of cracking. Patent Document 5 suggests a positive electrode active material for a nonaqueous secondary battery which is a lithium composite oxide in a powder form of monodispersed primary particles containing one kind of element selected from the group consisting of Co, Ni, and Mn, and lithium as a main component, and in which D50 is 3 μm to 12 μm, a specific surface area is 0.2 m2/g to 1.0 m2/g, a volume density is equal to or greater than 2.1 g/cm3, and an inflection point of a volume reduction rate in accordance with a Cooper plot method does not appear at 3 ton/cm2 or less.
Patent Document 6 relates to a lithium metal composite oxide powder that is expressed by LizNi1-wMwO2 (provided that, M represents at least one kind of metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga, and relationships of 0<w≦0.25 and 1.0≦z≦1.1 are satisfied), and suggests a positive electrode active material for a nonaqueous electrolyte secondary battery which includes primary particles of the lithium metal composite oxide powder, and secondary particles formed through agglomeration of a plurality of the primary particles, and in which the shape of the secondary particles is a spherical shape or an elliptical spherical shape, equal to or greater than 95% of the secondary particles has a particle size of equal to or less than 20 μm, an average particle size of the secondary particles is 7 μm to 13 μm, a tap density of the powder is equal to or greater than 2.2 g/cm3, an average volume of pores, which have an average diameter of 40 nm or less in pore size distribution measurement in accordance with a nitrogen absorption method, is 0.001 cm3/g to 0.008 cm3/g, and average crushing strength of the secondary particles is 15 MPa to 100 MPa.
Patent Document 7 suggests a lithium metal composite oxide having a layered structure. In the lithium metal composite oxide, a ratio of a crystallite diameter to an average powder particle size (D50), which is obtained through a laser diffraction and scattering particle size distribution measurement method after performing pulverization with a wet pulverizer and the like until D50 becomes 2 μm or less, granulation and drying with a thermal spray dryer, and calcining, is 0.05 to 0.20.